With the exception of some, but not all, newer GDI (Gasoline Direct Injection) engines, fuel injected engines have fuel injectors in the intake manifold upstream of the intake valves. Some GDI also have a combination of traditional injectors and direct injectors. It is inaccurate to say "the intake valve only ever sees filtered air."

https://en.wikipedia.org/wiki/Fuel_injection#Multi-point_inj...